TFTs are used as switching elements of respective pixels in active-matrix-driven display panels as typified by LCDs. Although amorphous silicon is used most commonly as a semiconductor layer, its mobility is as low as about 0.5 cm2/V·s. In view of this, in recent years, for use in large-size, high-resolution LCDs and organic light-emitting diodes (OLEDs; hereinafter also referred to as organic EL diodes) which enables high-quality display, oxide semiconductor TFTs using, for example, IGZO (In—Ga—Zn—O) whose mobility is higher than or equal to 10 cm2/V·s have been being developed. Materials as typified by IGZO are thought to provide such advantages as increase in aperture ratio and increase in the resolution of a display by virtue of their features that in general they have as wide band gaps as 3 eV and are transparent (i.e., have no absorptions in the visible range) (refer to JP-A-2007-81362 (corresponding to US2007/0057261A1), for example).
JP-A-2006-165529 (corresponding to US2006/0108636A1) discloses the configuration of a transistor which employs, as the material of an active layer, a microcrystal-containing amorphous oxide whose carrier density is lower than 1018 cm−3 and which contains at least one of In, Zn, and Ga.
JP-A-2003-298062 discloses the configuration of a thin-film transistor which uses, as an active layer, an oxide semiconductor film having ZnO as the main component.
JP-A-2007-81362 (corresponding to US2007/0057261A1) discloses the configuration of a thin-film transistor which uses a transparent semiconductor layer made of an oxide, nitride, or carbide substance.